Broadband impedance measuring device for flexible direct current feed-in system and control method

Abstract

The invention discloses a broadband impedance measuring device for a flexible direct current feed-in system and a control method, and relates to the technical field of broadband oscillation analysis of the flexible direct current feed-in system, and the broadband impedance measuring device comprises a controllable disturbance injection assembly, a fundamental wave shunting unit, a data acquisition unit and a central control unit. The controllable disturbance injection assembly is formed by connecting a plurality of controllable disturbance injection units in parallel and used for conducting disturbance injection on a tested system, the fundamental wave shunting unit is connected with the controllable disturbance injection assembly in parallel and used for bearing the fundamental wave current of the tested system, and through the multi-module parallel connection design, the controllable disturbance injection assembly can adapt to a high-voltage and large-current flexible direct current feed-in system; the problem that a traditional impedance measuring device cannot be matched with a high-voltage large-current scene is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of broadband oscillation analysis of a flexible DC feeding system, and in particular to a broadband impedance measurement device and a control method for a flexible DC feeding system. Background Technique

[0002] DC transmission technology has become one of the important ways for long-distance power transmission in China. Compared with traditional DC transmission technology, flexible DC transmission has the advantages of not requiring a large amount of reactive power support and not having commutation failure problems caused by thyristors. Therefore, it plays an important role in building a new power system. However, with the wide application of flexible DC transmission projects, the problem of broadband oscillation caused between it and the power grid has become increasingly prominent, seriously affecting the stability and reliability of the system.

[0003] The impedance parameters of the power grid and the impedance of the converter station of the flexible DC transmission system are the key parameters for analyzing and predicting the broadband oscillation of the flexible DC feeding system. Therefore, it is particularly important to develop a device that can accurately measure these impedance parameters. However, the flexible DC feeding system has the characteristics of high voltage and large current, and conventional impedance measurement devices are difficult to meet its measurement requirements. Most of the existing impedance measurement devices are designed for photovoltaic grid-connected systems and cannot be directly applied to the flexible DC feeding system, resulting in a large technical bottleneck in broadband oscillation analysis.

[0004] To solve the above problems, there is an urgent need for a broadband impedance measurement device and a control method suitable for a flexible DC feeding system. This device needs to have the ability to adapt to high voltage and large current and be able to accurately measure the impedance characteristics of the system within a broadband range. For this purpose, the present invention proposes a broadband impedance measurement device for a flexible DC feeding system based on multi-module parallel connection and its control method, aiming to provide reliable technical support for the broadband oscillation analysis of the flexible DC feeding system. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is: how to achieve broadband impedance measurement of a high-voltage and large-current flexible DC feeding system.

[0006] The above technical problem is solved by the following technical solution: The present invention proposes a broadband impedance measurement device for a flexible DC feeding system, which includes a controllable disturbance injection component, which is composed of a plurality of controllable disturbance injection units connected in parallel and is used for injecting disturbances into the system to be measured;

[0007] A fundamental wave shunt unit, including a switching switch composed of a plurality of anti-parallel IGBTs, the fundamental wave shunt unit is connected in parallel with the controllable disturbance injection component and is used to bear the fundamental wave current of the system to be measured;

[0008] A data acquisition unit, configured to acquire voltage and current data required by the impedance measurement device;

[0009] A central control unit, configured to receive the data uploaded by the data acquisition unit and form instructions;

[0010] The number of the controllable disturbance injection units and the anti-parallel IGBTs is calculated by the central control unit based on the data collected by the data acquisition unit.

[0011] In a preferred embodiment of the wide-band impedance measurement device for a flexible DC feeding system according to the present invention: The controllable disturbance injection unit includes an energy storage battery, an inverter circuit, a driving unit, and an output filter. Among them, one side of the driving unit is connected to the central control unit, and the other side is connected to the inverter circuit. The positive and negative electrodes of the energy storage battery are respectively connected to both sides of the input end of the inverter circuit. One side of the output port of the inverter circuit is connected to the output filter and then connected to the grid side of the system under test, and the other port is directly connected to the converter station side of the system under test through a wire.

[0012] In a preferred embodiment of the wide-band impedance measurement device for a flexible DC feeding system according to the present invention: The number of the controllable disturbance injection units is jointly determined by the fundamental wave current of the system under test and the injection capacity of a single controllable disturbance injection unit;

[0013] The number of the controllable disturbance injection units is expressed as:

[0014]

[0015] Wherein, It means to take the smallest integer N greater than as the number of the controllable disturbance injection units, I g is the fundamental wave current of the system under test, and I p is the injection capacity of a single controllable disturbance injection unit.

[0016] In a preferred embodiment of the wide-band impedance measurement device for a flexible DC feeding system according to the present invention: The fundamental wave shunt unit includes a resistor, an inductor, a capacitor, and a switching switch. One side of the switching switch is connected to the grid side of the system under test, the other side is connected to the inductor, the other side of the inductor is connected to the capacitor, the other side of the capacitor is connected to the resistor, and the other end of the resistor is connected to the converter station side of the system under test.

[0017] In a preferred embodiment of the wide-band impedance measurement device for a flexible DC feeding system according to the present invention: The resistor is used to prevent the fundamental wave shunt unit from being short-circuited with the controllable disturbance injection unit in the circuit;

[0018] The inductor and the capacitor are used to form a fundamental frequency resonance.

[0019] In a preferred embodiment of the broadband impedance measuring device for a flexible DC feeding system according to the present invention: The operating frequency of the system under test is expressed as:

[0020]

[0021] where L d is the value of the inductor, C d is the value of the capacitor, and f d is the operating frequency of the system under test.

[0022] In a preferred embodiment of the broadband impedance measuring device for a flexible DC feeding system according to the present invention: The switching switch is composed of a plurality of anti-parallel IGBTs, and the switching switch is used for controlling the input and cut-off of the fundamental wave shunt unit;

[0023] The number of the anti-parallel IGBTs is determined by the current of the flexible DC feeding system under test and satisfies

[0024]

[0025] where n is the number of the anti-parallel IGBTs, I g is the current of the flexible DC feeding system under test, and I IGBT is the rated current of the IGBT used.

[0026] In a preferred embodiment of the broadband impedance measuring device for a flexible DC feeding system according to the present invention: The data acquisition unit acquires a large amount of voltage and current information of the device itself and the system under test by setting voltage sensors and current sensors.

[0027] In a preferred embodiment of the broadband impedance measuring device for a flexible DC feeding system according to the present invention: The central control unit is used to receive the data uploaded by the data acquisition unit and form a first control instruction and a second control instruction;

[0028] The first control instruction is used to control the input and cut-off of the fundamental wave shunt unit, and the second control instruction is used to control the controllable disturbance injection component to perform disturbance injection.

[0029] Another object of the present invention is to provide a control method, which is applied to the broadband impedance measuring device for a flexible DC feeding system, including:

[0030] S1: Based on the data fed back by the data acquisition unit, the central control unit calculates the required number of the controllable disturbance injection units and the number of the anti-parallel IGBTs;

[0031] S2: The central control unit outputs a first control instruction to control the anti-parallel IGBT to connect the fundamental wave shunt unit to the system under test;

[0032] S3: The central control unit outputs a second control instruction, and the controllable disturbance injection component injects disturbances of various frequencies into the system under test according to the instruction;

[0033] S4: After the injection of disturbances of various frequencies is completed, the central control unit executes the second control instruction to withdraw the controllable disturbance injection component from operation;

[0034] S5: After the controllable disturbance injection component withdraws from operation, the central control unit outputs a first control instruction to withdraw the fundamental wave shunt unit from the system under test.

[0035] The beneficial effects of the present invention are as follows: 1. Through the multi-module parallel design, it can adapt to the flexible DC feeding system with high voltage and large current, and solves the problem that the traditional impedance measurement device cannot match the high-voltage and large-current scenarios;

[0036] 2. By injecting broadband controllable voltage disturbances into the system under test through multiple controllable disturbance injection units, a wider frequency range can be covered, so as to obtain the impedance characteristics of the flexible DC feeding system more comprehensively. This helps to accurately analyze the dynamic behavior of the system at different frequencies and provides more accurate data support for broadband oscillation analysis;

[0037] 3. The design of the fundamental wave shunt unit effectively solves the problem of interference of the fundamental wave current on impedance measurement. By using resistors, it is avoided that the fundamental wave shunt unit and the controllable disturbance injection unit are short-circuited in the fundamental frequency equivalent circuit, preventing current over-limit; at the same time, the inductor and capacitor form a fundamental frequency resonance to ensure that the fundamental wave current of the system passes through the fundamental wave shunt unit smoothly, ensuring that the impedance measurement of other frequencies is not affected, and improving the accuracy and reliability of the measurement;

[0038] 4. The controllable disturbance injection units are connected in a multi-module parallel manner, and the number of units put into operation can be flexibly adjusted according to the fundamental wave current of the system under test and the injection capacity of a single unit. This modular design not only improves the output capacity of the disturbance device, but also facilitates the expansion and maintenance of the device, enabling it to adapt to flexible DC feeding systems of different scales and requirements;

[0039] 5. The adjustable inductor in the fundamental wave shunt unit can be adjusted according to the change of the operating frequency of the system under test to meet the requirements of the system fundamental frequency. This enables the device to still maintain good impedance measurement results in the face of system frequency fluctuations, enhancing the adaptability of the device to different operating conditions;

[0040] 6. Multiple controllable disturbance injection units are connected in parallel and then connected to the system under test in series, effectively reducing the voltage stress on the devices in a single controllable disturbance injection unit. This helps improve the stability and lifespan of the device, and also facilitates the selection of more economical devices, reducing the manufacturing cost of the device;

[0041] 7. The data acquisition system can comprehensively collect the voltage and current information of the device itself and the system under test by arranging voltage and current sensors, and upload it to the central controller after filtering. The central controller generates control instructions based on the collected data to achieve precise control of the fundamental wave shunt unit and the controllable disturbance injection unit. This efficient data acquisition and processing mechanism ensures that the device can respond to changes in the system state in real time, improving the efficiency and accuracy of measurement. Description of the Drawings

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention and do not limit the present invention. Among them:

[0043] Figure 1 Shows the schematic diagram of the wide-band impedance measurement device for the flexible DC feeding system;

[0044] Figure 2 Shows the circuit diagram of the controllable disturbance injection unit of the wide-band impedance measurement device for the flexible DC feeding system;

[0045] Figure 3 Shows the fundamental wave shunt circuit diagram of the controllable disturbance injection unit;

[0046] Figure 4 Shows Figure 3 The composition diagram of the switching switch;

[0047] Figure 5 Shows the schematic diagram of the control instruction generation of the wide-band impedance measurement device for the flexible DC feeding system;

[0048] Figure 6 Shows the execution flowchart of the control method. Detailed Embodiments

[0049] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below in conjunction with the detailed embodiments and the drawings.

[0050] The terms used in the present invention are those general terms that are currently widely used in the art in consideration of the functions of the present invention. However, these terms may vary according to the intentions of those of ordinary skill in the art, precedents, or new technologies in the art. In addition, specific terms may be selected by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the present invention. Therefore, the terms used in the specification should not be understood as simple names, but based on the meanings of the terms and the overall description of the present invention.

[0051] Referring to Figure 1 , as an embodiment of the present invention, this embodiment provides a wide-band impedance measurement device for a flexible DC feeding system, including a controllable disturbance injection component 1, a fundamental wave shunt unit 2, a data acquisition unit 3, and a central control unit 4.

[0052] Specifically, the controllable disturbance injection component 1 is composed of a plurality of controllable disturbance injection units 10 connected in parallel, and is used for injecting disturbances into the system to be measured;

[0053] The fundamental wave shunt unit 2 includes a switching switch 23 composed of a plurality of anti-parallel IGBTs, and is connected in parallel with the controllable disturbance injection component 1, and is used to bear the fundamental wave current of the system to be measured;

[0054] The data acquisition unit 3 is used to collect the voltage and current data required by the impedance measurement device;

[0055] The central control unit 4 is used to receive the data uploaded by the data acquisition unit 3 and form instructions;

[0056] The number of the controllable disturbance injection units 10 and the anti-parallel IGBTs is calculated by the central control unit 4 based on the data collected by the data acquisition unit 3

[0057] The central control unit 4 can receive the data of the data acquisition unit 3, and can send instructions to the controllable disturbance injection component 1 and the fundamental wave shunt unit 2 respectively to measure the system impedance.

[0058] Preferably, the controllable disturbance injection units 10 are connected in parallel. By connecting multiple controllable disturbance injection units 10 in parallel, the disturbance output ability of the disturbance device can be improved, which is more convenient for modular design; after the controllable disturbance injection units 10 are connected in parallel, they are connected in series between the converter station of the flexible DC transmission system to be measured and the power grid. The series connection method can reduce the voltage stress of the devices in the controllable disturbance injection units 10.

[0059] Referring to Figure 2, is the main topology circuit of the controllable disturbance injection unit 10 of the wide-band impedance measurement device for the flexible DC feeding system, which is used to inject wide-band controllable voltage disturbances into the measured flexible DC feeding system; to avoid current imbalance problems, all parameters in the main circuit and control circuit of the controllable disturbance injection unit 10 are kept consistent. Specifically, the controllable disturbance injection unit 10 includes an energy storage battery 100, an inverter circuit 101, a driving unit 102, and an output filter 103. Among them, one side of the driving unit 102 is connected to the central control unit 4, and the other side is connected to the inverter circuit 101. The positive and negative poles of the energy storage battery 100 are respectively connected to both sides of the input end of the inverter circuit 101. One side of the output port of the inverter circuit 101 is connected to the output filter 103 and then connected to the grid side of the measured system, and the other port is directly connected to the converter station side of the measured system through a wire. The energy storage battery 100 is used to provide DC voltage support for the controllable disturbance injection unit 10. Different numbers of battery packs need to be put into use according to the current size of the test system and the difference in disturbance injection requirements to meet the disturbance injection needs;

[0060] The function of the inverter circuit 101 is to convert the direct current provided by the battery into AC disturbance signals of various frequencies according to the control instruction (driving signal);

[0061] The output filter 103 is composed of a single inductor, which is used to filter out the high-frequency switching signals generated by the inverter circuit 101 to reduce the high-frequency switching harmonics injected into the system and improve the signal-to-noise ratio of the output disturbance signals of various frequencies.

[0062] Preferably, the number of the controllable disturbance injection units 10 is jointly determined by the fundamental wave current of the measured system and the injection capacity of a single controllable disturbance injection unit 10;

[0063] The number of the controllable disturbance injection units 10 is expressed as:

[0064]

[0065] Among them, means taking the smallest integer greater than , N is the number of the controllable disturbance injection units 10, I g is the fundamental wave current of the measured system, and I p is the injection capacity of a single controllable disturbance injection unit 10.

[0066] Referring to Figure 3 , the fundamental wave shunt unit 2 is connected to the measured system in a way that is parallel to the controllable disturbance injection unit 10, and its two ends are respectively connected to the converter station and the grid of the measured flexible DC transmission system.

[0067] Preferably, the fundamental wave shunt unit 2 includes a resistor 20, an inductor 21, a capacitor 22, and a switching switch 23. One side of the switching switch 23 is connected to the grid side of the system under test, and the other side is connected to the inductor 21. The other side of the inductor 21 is connected to the capacitor 22, the other side of the capacitor 22 is connected to the resistor 20, and the other end of the resistor 20 is connected to the converter station side of the system under test.

[0068] Preferably, the resistor 20 is used to prevent the fundamental wave shunt unit 2 from short - circuiting with the controllable disturbance injection unit 10 in the circuit;

[0069] The inductor 21 and the capacitor 22 are used to form a fundamental frequency resonance.

[0070] Preferably, the operating frequency of the system under test is expressed as:

[0071]

[0072] where, L d is the value of the inductor 21, C d is the value of the capacitor 22, f d is the operating frequency of the system under test. When the system operating frequency is inconsistent with the nominal frequency, the value of the inductor 21 can be adjusted to satisfy the above equation. If the device is designed according to the system nominal frequency of 50 Hz, set L d = 3.18 mH and C d = 3.18 mF; if the actual system operates at 50.5 Hz, L d = 3.186 mH, and the capacitor remains C d = 3.18 mF. Usually, to achieve a better disturbance effect, it is required that the value of L d takes the maximum value under allowable conditions.

[0073] Preferably, the switching switch 23 is composed of several antiparallel IGBTs, and the switching switch 23 is used to control the input and cut - off of the fundamental wave shunt unit 2;

[0074] The number of antiparallel IGBTs is determined by the current of the flexible DC feeding system under test and satisfies

[0075]

[0076] where, n is the number of antiparallel IGBTs, I g is the current of the flexible DC feeding system under test, I IGBT is the rated current of the IGBT used. For example, if the current of the flexible DC feeding system under test I g = 1000 A and the selected IGBT rated current is 50 A, then the number of antiparallel IGBTs should be n = 40 to ensure the normal operation of the fundamental wave shunt unit during conduction and no current passing through the fundamental wave shunt power supply after cut - off.

[0077] Preferably, the data acquisition unit 3 collects a large amount of voltage and current information of the device itself and the system under test by setting voltage sensors and current sensors. The data acquisition unit 3 collects a large amount of voltage and current information of the device itself and the system under test by arranging voltage and current sensors, including the access point voltage u of the device pcc of the system under test, current i g , output voltage u of the controllable disturbance injection unit 10 p and output currents i of each unit p1 , i p2 ...i pn , current i of the fundamental wave shunt unit d and other key information, and uploads it to the central controller after filtering processing.

[0078] Preferably, the central control unit 4 is used to receive the data uploaded by the data acquisition unit 3 and form a first control instruction and a second control instruction;

[0079] The first control instruction is used to control the connection and disconnection of the fundamental wave shunt unit 2, and the second control instruction is used to control the controllable disturbance injection component 1 to perform disturbance injection.

[0080] Referring to Figure 4 and Figure 5 , the present invention also provides a control method for a wide-band impedance measurement device of a flexible DC feeding system, and this method can control the above-mentioned measurement device. The specific steps are as follows: S1: Based on the data fed back by the data acquisition unit 3, the central control unit 4 calculates the required number of controllable disturbance injection units 10 and the number of anti-parallel IGBTs;

[0081] S2: The central control unit 4 outputs a first control instruction to control the anti-parallel IGBT to connect the fundamental wave shunt unit 2 to the system under test;

[0082] S3: The central control unit 4 outputs a second control instruction, and the controllable disturbance injection component 1 injects disturbances of each frequency into the system under test according to the instruction;

[0083] S4: After the injection of each frequency disturbance is completed, the central control unit 4 executes the second control instruction to withdraw the controllable disturbance injection component 1 from operation;

[0084] S5: After the controllable disturbance injection component 1 withdraws from operation, the central control unit 4 outputs a first control instruction to withdraw the fundamental wave shunt unit 2 from the system under test.

[0085] Finally, it should be noted that the methods and devices described in detail above are only embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A broadband impedance measurement device for a flexible DC feed system, characterized in that: include, A controllable disturbance injection component (1) is composed of a plurality of controllable disturbance injection units (10) connected in parallel and is used for injecting disturbance into a system under test; A fundamental wave current shunting unit (2) comprises a switching switch (23) composed of a plurality of anti-parallel IGBTs, wherein the fundamental wave current shunting unit (2) is connected in parallel with the controllable disturbance injection component (1) and is used to bear the fundamental wave current of the system under test; A data acquisition unit (3), used for acquiring voltage and current data required by the impedance measurement device; A central control unit (4) is used to receive the data uploaded by the data acquisition unit (3) and generate instructions; The controllable disturbance injection unit (10) and the number of anti-parallel IGBTs are calculated by the central control unit (4) based on the data collected by the data acquisition unit (3).

2. The flexible DC feed system broadband impedance measurement device according to claim 1, characterized in that: The controllable disturbance injection unit (10) comprises an energy storage battery (100), an inverter circuit (101), a drive unit (102) and an output filter (103), wherein one side of the drive unit (102) is connected to the central control unit (4), and the other side is connected to the inverter circuit (101); the positive and negative electrodes of the energy storage battery (100) are respectively connected to the two sides of the input end of the inverter circuit (101); one side of the output port of the inverter circuit (101) is connected to the output filter (103) and then connected to the power grid side of the system under test; and the other port is directly connected to the converter station side of the system under test through a wire.

3. The flexible DC feed system broadband impedance measurement device according to claim 2, characterized in that: The number of the controllable disturbance injection units (10) is determined by the fundamental current of the system under test and the injection capacity of a single controllable disturbance injection unit (10); The number of the controllable disturbance injection units (10) is expressed as: in, Indicates greater than The smallest integer, N is the number of controllable disturbance injection units (10), I g is the fundamental current of the system under test, I p is the injection capacity of a single controllable disturbance injection unit (10).

4. The flexible DC feed system wideband impedance measurement device according to claim 3, characterized in that: The fundamental wave shunting unit (2) further comprises a resistor (20), an inductor (21) and a capacitor (22); One side of the switching switch (23) is connected to the grid side of the system under test, and the other side is connected to the inductor (21), the other side of the inductor (21) is connected to the capacitor (22), the other side of the capacitor (22) is connected to the resistor (20), and the other end of the resistor (20) is connected to the converter station side of the system under test.

5. The flexible DC feed system broadband impedance measurement device according to claim 4, characterized in that: The resistor (20) is used to prevent the fundamental wave shunting unit (2) and the controllable disturbance injection unit (10) from being short-circuited in the circuit; The inductor (21) and the capacitor (22) are used to form fundamental frequency resonance.

6. The flexible DC feed system broadband impedance measurement device according to claim 5, characterized in that: The operating frequency of the system under test is expressed as: Among them, L d is the value of the inductor (21), C d is the value of the capacitor (22), f d is the operating frequency of the system under test.

7. The flexible DC feed system broadband impedance measurement device according to claim 6, characterized in that: The switching switch (23) is composed of a plurality of anti-parallel IGBTs, and the switching switch (23) is used for controlling the switching on and off of the fundamental wave shunt unit (2); The number of the anti-parallel IGBTs is determined by the current of the flexible DC feed-in system to be tested and meets the following requirements: Where n is the number of anti-parallel IGBTs, I g is the current of the flexible DC feed-in system under test, I IGBT is the rated current of the IGBT used.

8. The flexible DC feed system broadband impedance measurement device according to claim 7, characterized in that: The data acquisition unit (3) collects a large amount of voltage and current information of the device itself and the system under test by arranging voltage sensors and current sensors.

9. The flexible DC feed system broadband impedance measurement device according to claim 8, characterized in that: The central control unit (4) is used to receive the data uploaded by the data acquisition unit (3) and form a first control instruction and a second control instruction; The first control instruction is used to control the activation and deactivation of the fundamental wave shunt unit (2), and the second control instruction is used to control the controllable disturbance injection component (1) to perform disturbance injection.

10. A control method, applied to the flexible DC feed system wide-band impedance measurement device according to claims 1 to 9, comprising: S1: Based on the data fed back by the data acquisition unit (3), the central control unit (4) calculates the required number of the controllable disturbance injection units (10) and the number of the anti-parallel IGBTs; S2: the central control unit (4) outputs a first control instruction to control the anti-parallel IGBT to connect the fundamental wave shunt unit (2) to the system under test; S3: the central control unit (4) outputs a second control instruction, and the controllable disturbance injection component (1) injects various frequency disturbances into the system under test according to the instruction; S4: after each frequency disturbance injection is completed, the central control unit (4) executes a second control instruction to stop the controllable disturbance injection component (1) from operating; S5: After the controllable disturbance injection component (1) stops running, the central control unit (4) outputs a first control instruction to remove the fundamental wave shunt unit (2) from the system under test.

Images