Wideband impedance online measurement method and system of power grid side and equipment side, electronic equipment and storage medium

Abstract

The invention discloses a broadband impedance online measurement method and system for a power grid side and an equipment side, electronic equipment and a storage medium, and the method comprises the steps: respectively measuring a first voltage and a first current at a common point when a disturbance current is injected at the power grid side and the equipment side; calculating a second voltage and a second current under the disturbance current value when the disturbance current is not injected; the impedance is a ratio of a voltage difference and a current difference, the voltage difference is a difference between the first voltage and the second voltage, and the current difference is a difference between the first current and the second current. According to the method, under the condition that a power system operates normally, the FFT algorithm and the impedance calculation method are combined, the power grid side impedance and the equipment side impedance are measured at the same time, and the stability margin of the system can be analyzed on line according to the impedance measurement result.

Description

Technical Field

[0001] The present invention relates to the technical field of broadband impedance measurement, and in particular to a method, system, electronic device and storage medium for online broadband impedance measurement on a power grid side and a device side. Background Art

[0002] With the increase in installed capacity of new energy, the application scale of power electronic equipment is also expanding, and the power system presents "double high" characteristics. Due to the volatility and randomness of new energy power generation, the safety and stability of the power system characterized by broadband oscillation is becoming increasingly prominent.

[0003] Impedance analysis is often used to analyze broadband oscillation problems in renewable energy power generation systems. The impedance model has a clear physical meaning. The small signal stability of the system is analyzed through the Nyquist criterion and the Bode diagram to determine whether broadband oscillation occurs. However, due to the complex structure of the real power system, the diversity of power electronic equipment, and the random operating conditions, the impedance of the power system and equipment cannot be calculated. It is a typical "black box" system, so there is a lack of impedance model analysis of the conditions for the generation of oscillations. Not only that, the existing impedance measurement methods cannot simultaneously obtain the broadband impedance of the grid side and the equipment side. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method, system, electronic device and storage medium for online measurement of broadband impedance on the grid side and the equipment side, which can realize real-time measurement of impedance on the equipment side and the grid side without bearing the fundamental current of the power system being measured and has little impact on the running equipment.

[0005] Technical solution: In the first aspect, the broadband impedance online measurement method on the grid side and the device side of the present invention comprises the following steps:

[0006] For the grid side and the device side, respectively measuring a first voltage and a first current when a disturbance current is injected at a common point, and calculating a second voltage and a second current at a disturbance current value when no disturbance current is injected;

[0007] The broadband impedance is measured according to the first voltage, the first current, the second voltage and the second current. The broadband impedance is the ratio of the voltage difference to the current difference, wherein the voltage difference is the difference between the first voltage and the second voltage, and the current difference is the difference between the first current and the second current.

[0008] Furthermore, before respectively measuring the first voltage and the first current when the disturbance current is injected at the common point, the method further comprises: connecting the disturbance current output device in parallel to the common point of the power grid system to inject the disturbance current.

[0009] Furthermore, the amplitude of the disturbance current is smaller than a preset ratio of the fundamental wave amplitude.

[0010] Furthermore, the amplitude of the disturbance current is less than 5% of the fundamental wave amplitude.

[0011] Furthermore, the method further comprises: performing FFT analysis and positive-negative sequence decomposition on the first voltage, the second voltage, the first current and the second current to obtain a first positive sequence voltage, a second positive sequence voltage, a first positive sequence current, a second positive sequence current and a first negative sequence voltage, a second negative sequence voltage, a first negative sequence current and a second negative sequence current;

[0012] The positive sequence impedance is the ratio of the difference between the first positive sequence voltage and the second positive sequence voltage to the difference between the first positive sequence current and the second positive sequence current;

[0013] The negative sequence impedance is a ratio of a difference between a first negative sequence voltage and a second negative sequence voltage to a difference between a first negative sequence current and a second negative sequence current.

[0014] In a second aspect, the broadband impedance online measurement system on the grid side and the equipment side of the present invention comprises:

[0015] The post-disturbance injection calculation unit measures, for the grid side and the device side, respectively, a first voltage and a first current when the disturbance current is injected at the common point;

[0016] The calculation unit before disturbance injection calculates, for the grid side and the device side, respectively, the second voltage and the second current at the disturbance current value when the disturbance current is not injected;

[0017] The impedance calculation unit is used to measure the broadband impedance according to the first voltage, the first current, the second voltage and the second current, wherein the broadband impedance is the ratio of the voltage difference to the current difference, wherein the voltage difference is the difference between the first voltage and the second voltage, and the current difference is the difference between the first current and the second current.

[0018] Furthermore, in the disturbance injection post-calculation unit, a disturbance current output device is connected in parallel to a common point of the power grid system to inject the disturbance current.

[0019] Furthermore, in the calculation unit after the disturbance is injected, the amplitude of the disturbance current is smaller than a preset ratio of the fundamental wave amplitude.

[0020] Furthermore, in the calculation unit after the disturbance is injected, the amplitude of the disturbance current is less than 5% of the fundamental wave amplitude.

[0021] Further, in the impedance calculation unit, FFT analysis and positive-negative sequence decomposition are performed on the first voltage, the second voltage, the first current and the second current to obtain a first positive-sequence voltage, a second positive-sequence voltage, a first positive-sequence current, a second positive-sequence current and a first negative-sequence voltage, a second negative-sequence voltage, a first negative-sequence current and a second negative-sequence current;

[0022] The positive sequence impedance is the ratio of the difference between the first positive sequence voltage and the second positive sequence voltage to the difference between the first positive sequence current and the second positive sequence current;

[0023] The negative sequence impedance is a ratio of a difference between a first negative sequence voltage and a second negative sequence voltage to a difference between a first negative sequence current and a second negative sequence current.

[0024] In a third aspect, the electronic device described in the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the computer program is loaded into the processor, the online measurement method for broadband impedance on the grid side and the device side is implemented.

[0025] In a fourth aspect, the computer-readable storage medium of the present invention stores a computer program, and when the computer program is executed by a processor, the method for online measurement of broadband impedance on the grid side and the device side is implemented.

[0026] Beneficial effect: Compared with the prior art, the advantages of the present invention are: the impedance online measurement method based on current disturbance of the present invention can combine the FFT algorithm and the impedance calculation method to measure the grid side impedance and the device side impedance at the same time when the power system is operating normally; the stability margin of the system can be analyzed online based on the impedance measurement results. At the same time, the broadband current disturbance online measurement of the device side and grid side impedance has lower current capacity requirements for the measuring equipment than the series disturbance voltage source, and has advantages in equipment volume and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of a disturbance current injection according to an embodiment of the present invention;

[0028] Figure 2 is an amplitude-frequency characteristic diagram of impedance in an embodiment of the present invention;

[0029] Figure 3 4 is a phase-frequency characteristic diagram of impedance in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0031] The method for online measurement of broadband impedance on the grid side and the equipment side is to connect the disturbance current output device in parallel to the common point of the grid system. When the system is operating normally, a disturbance current much smaller than the fundamental frequency current is injected into the common point, and the voltage and current flowing to both ends are measured. FFT analysis is first performed, and then the positive and negative sequence voltage and current components are obtained by positive and negative sequence decomposition. The amplitude and phase information of the voltage and current at the disturbance frequency are extracted, and the amplitude and phase of the port impedance at the disturbance frequency on both sides of the common point can be simultaneously measured and calculated. In this way, the broadband impedance of the equipment side and the grid side can be measured online. On this basis, impedance analysis can be further performed online to calculate the system stability margin. Specifically, the following steps are included.

[0032] Step 1: Inject disturbance current into the common point of the power grid system.

[0033] The disturbance current output device of this embodiment is a wide-band disturbance current output device, which is composed of a power electronic switch device and a controller, etc., and can absorb 50Hz current and obtain a wide-band disturbance current output of any amplitude through modulation. The use of power electronic equipment to achieve wide-band disturbance current output has the advantages of controllable disturbance frequency and amplitude.

[0034] like Figure 1 As shown in the figure, the broadband disturbance current output device is connected in parallel to the common point of the power grid system. The device does not need to bear the influence of the fundamental current. The capacity of the object to be measured can be much larger than the capacity of the measuring device. The capacity ratio can reach 20:1, which is better than the impedance measurement method of the disturbance voltage. The amplitude of the injected broadband disturbance current is less than 5% of the fundamental amplitude (|I p |<5%|I0|), which has little impact on the protection of the power system.

[0035] Step 2: Sequence impedance measurement.

[0036] Measure the voltage and current on the grid side and the equipment side, perform FFT processing on the voltage and current, decompose the positive and negative sequence at the disturbance frequency, and obtain the positive and negative sequence components of the voltage and current at the disturbance frequency; calculate the frequency domain impedance at this frequency:

[0037]

[0038] Among them, f p is the disturbance frequency; Z(j2πf p ) is the impedance of the passive component; U(j2πf p ) is the voltage on the passive component; I(j2πf p ) is the current flowing through the passive components.

[0039] Step 3, impedance measurement to eliminate interference from the output of active devices.

[0040] When measuring the impedance of active devices such as power electronic equipment, there are many interferences. It is necessary to first detect the amplitude and phase of the voltage and current on the device under test at the disturbance frequency when no disturbance is injected, and then inject the current at the disturbance frequency. Then, based on the difference between the voltage and current after and before the disturbance injection, the impedance at this frequency can be calculated, that is:

[0041]

[0042] In the formula, f p is the measurement frequency, which is the same as the disturbance frequency; Z A (j2πf p ) is the impedance of the active device; ΔU(j2πf p ) is the voltage difference between the active device after and before the disturbance injection; ΔI(j2πf p ) is the difference between the current flowing through the active device after and before the disturbance injection.

[0043] Step 4: broadband impedance measurement on the grid side and the equipment side.

[0044] The voltage and current on the grid side are processed by FFT analysis to obtain the disturbance components of the voltage and current, and then the positive and negative sequence decomposition is performed to calculate the positive and negative sequence impedance on the grid side at the disturbance frequency:

[0045]

[0046] In the formula, f pp 、f pn are the positive sequence frequency and negative sequence frequency of the disturbance frequency respectively; Z gp (j2πf pp ), Z gn (j2πf pn ) are the positive sequence impedance and negative sequence impedance of the grid side respectively; since the voltage of the grid side is the same as the voltage at the common point, this embodiment uses the voltage at the common point for calculation, ΔU p (j2πf pp ), ΔU n (j2πf pn ) are the difference between the positive sequence voltage and the negative sequence voltage at the common point after and before the disturbance injection, respectively; ΔI gp (j2πf pp ), ΔI gn (j2πf pn ) are the difference between the positive sequence current and the negative sequence current flowing through the power grid after and before the disturbance injection, respectively.

[0047] The voltage and current on the device side are processed by FFT analysis to obtain the disturbance components of the voltage and current, and then the positive and negative sequence decomposition is performed to calculate the positive and negative sequence impedance on the device side at the disturbance frequency:

[0048]

[0049] In the formula, Z dp (j2πf pp ), Z dn (j2πf pn ) are respectively the positive sequence impedance and negative sequence impedance of the device side; since the voltage on the device side is the same as the voltage at the common point, the voltage at the common point is used for calculation in this embodiment; ΔI dp (j2πf pp ), ΔI dn (j2πf pn ) are the difference between the positive sequence current and the negative sequence current flowing through the equipment side after and before the disturbance injection, respectively.

[0050] The method of the present invention is described below through specific experiments.

[0051] like Figure 1 The figure shows the wiring diagram of the power system of this embodiment. The power system is composed of a grid-connected converter-weak grid with a grid voltage of 380V. Three AC / DC converters are connected, of which AC / DC5 works in DC voltage regulation mode, AC / DC1 works in AC voltage regulation mode, and AC / DC2 works in power mode, forming a 380V common point. An inductor L=1mH is used to simulate the grid impedance. The grid impedance can be changed by changing the inductor. At this time, the current flowing through the common point is 60A.

[0052] In order to accurately verify the effect of the present invention on measuring the impedance of the device side and the grid side, first, when the grid impedance is small, current disturbances of multiple disturbance frequencies are sequentially emitted, and the disturbance current amplitude is 3A; then the impedance of the device side and the grid side is calculated, and the amplitude-frequency characteristics and phase-frequency characteristics of the impedance on both sides can be obtained, such as Figure 2 and Figure 3 As shown in the figure, it can be seen that the present invention can simultaneously measure the impedance of the grid side and the device side, and obtain its amplitude-frequency characteristics and phase-frequency characteristics. It has the advantage of online measurement of the impedance of the grid side and the device side with small amplitude disturbance.

[0053] The broadband impedance online measurement system on the grid side and the equipment side of the present invention comprises:

[0054] The post-disturbance injection calculation unit measures, for the grid side and the device side, respectively, a first voltage and a first current when the disturbance current is injected at the common point;

[0055] The calculation unit before disturbance injection calculates, for the grid side and the device side, respectively, the second voltage and the second current at the disturbance current value when the disturbance current is not injected;

[0056] The impedance calculation unit is used to measure the broadband impedance according to the first voltage, the first current, the second voltage and the second current, wherein the broadband impedance is the ratio of the voltage difference to the current difference, wherein the voltage difference is the difference between the first voltage and the second voltage, and the current difference is the difference between the first current and the second current.

[0057] Furthermore, in the disturbance injection post-calculation unit, a disturbance current output device is connected in parallel to a common point of the power grid system to inject the disturbance current.

[0058] Furthermore, in the calculation unit after the disturbance is injected, the amplitude of the disturbance current is less than 5% of the fundamental wave amplitude.

[0059] Further, the impedance calculation unit performs FFT analysis and positive-negative sequence decomposition on the first voltage, the second voltage, the first current and the second current to obtain a first positive sequence voltage, a second positive sequence voltage, a first positive sequence current, a second positive sequence current and a first negative sequence voltage, a second negative sequence voltage, a first negative sequence current and a second negative sequence current;

[0060] The positive sequence impedance is the ratio of the difference between the first positive sequence voltage and the second positive sequence voltage to the difference between the first positive sequence current and the second positive sequence current;

[0061] The negative sequence impedance is a ratio of a difference between a first negative sequence voltage and a second negative sequence voltage to a difference between a first negative sequence current and a second negative sequence current.

[0062] The electronic device described in the present invention includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded into the processor, the online measurement method for broadband impedance on the grid side and the device side is implemented.

[0063] The computer-readable storage medium of the present invention stores a computer program, and when the computer program is executed by a processor, the method for online measurement of broadband impedance on the grid side and the device side is implemented.

[0064] The computer-readable storage medium may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage devices, magnetic disk storage devices or other magnetic storage devices, flash memory or any other medium that can be used to store program codes in the form of instructions or data structures and can be accessed by a computer. The processor is used to execute the computer program stored in the memory to implement the various steps in the method involved in the above embodiments.

Claims

1. A broadband impedance online measurement method for a power grid side and a device side, characterized in that: The steps include: For the grid side and the device side, respectively measuring a first voltage and a first current when a disturbance current is injected at a common point, and calculating a second voltage and a second current at a disturbance current value when no disturbance current is injected; The broadband impedance is measured according to the first voltage, the first current, the second voltage and the second current. The broadband impedance is the ratio of the voltage difference to the current difference, wherein the voltage difference is the difference between the first voltage and the second voltage, and the current difference is the difference between the first current and the second current.

2. The method for online measurement of broadband impedance on the grid side and the equipment side according to claim 1, characterized in that: Before respectively measuring the first voltage and the first current when the disturbance current is injected at the common point, the method further includes: The disturbance current output device is connected in parallel to the common point of the power grid system to inject the disturbance current.

3. The method for online measurement of broadband impedance on the grid side and the equipment side according to claim 1, characterized in that: The amplitude of the disturbance current is smaller than a preset ratio of the fundamental wave amplitude.

4. The method for online measurement of broadband impedance on the network side and the device side according to claim 3, characterized in that: The amplitude of the disturbance current is less than 5% of the fundamental wave amplitude.

5. The method for online measurement of broadband impedance on the grid side and the equipment side according to claim 1, characterized in that: The method further includes: performing FFT analysis and positive-negative sequence decomposition on the first voltage, the second voltage, the first current and the second current to obtain a first positive sequence voltage, a second positive sequence voltage, a first positive sequence current, a second positive sequence current and a first negative sequence voltage, a second negative sequence voltage, a first negative sequence current and a second negative sequence current; The positive sequence impedance is the ratio of the difference between the first positive sequence voltage and the second positive sequence voltage to the difference between the first positive sequence current and the second positive sequence current; The negative sequence impedance is a ratio of a difference between a first negative sequence voltage and a second negative sequence voltage to a difference between a first negative sequence current and a second negative sequence current.

6. A broadband impedance online measurement system for the power grid side and the equipment side, characterized in that: include: The post-disturbance injection calculation unit measures, for the grid side and the device side, respectively, a first voltage and a first current when the disturbance current is injected at the common point; The calculation unit before disturbance injection calculates, for the grid side and the device side, respectively, the second voltage and the second current at the disturbance current value when the disturbance current is not injected; The impedance calculation unit is used to measure the broadband impedance according to the first voltage, the first current, the second voltage and the second current, wherein the broadband impedance is the ratio of the voltage difference to the current difference, wherein the voltage difference is the difference between the first voltage and the second voltage, and the current difference is the difference between the first current and the second current.

7. The broadband impedance online measurement system for the grid side and the equipment side according to claim 6, characterized in that: In the disturbance injection post-calculation unit, the disturbance current output device is connected in parallel to the common point of the power grid system to inject the disturbance current.

8. The broadband impedance online measurement system for the grid side and the equipment side according to claim 6, characterized in that: In the disturbance injection post-calculation unit, the amplitude of the disturbance current is smaller than a preset ratio of the fundamental wave amplitude.

9. The broadband impedance online measurement system for the grid side and the equipment side according to claim 8, characterized in that: In the calculation unit after the disturbance is injected, the amplitude of the disturbance current is less than 5% of the fundamental wave amplitude.

10. The broadband impedance online measurement system for the grid side and the equipment side according to claim 6, characterized in that: In the impedance calculation unit, the first voltage, the second voltage, the first current and the second current are subjected to FFT analysis and positive-negative sequence decomposition to obtain a first positive-sequence voltage, a second positive-sequence voltage, a first positive-sequence current, a second positive-sequence current and a first negative-sequence voltage, a second negative-sequence voltage, a first negative-sequence current and a second negative-sequence current; The positive sequence impedance is the ratio of the difference between the first positive sequence voltage and the second positive sequence voltage to the difference between the first positive sequence current and the second positive sequence current; The negative sequence impedance is a ratio of a difference between a first negative sequence voltage and a second negative sequence voltage to a difference between a first negative sequence current and a second negative sequence current.

11. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the computer program is loaded into the processor, the method for online measurement of broadband impedance on the grid side and the device side according to any one of claims 1 to 5 is implemented.

12. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for online measurement of broadband impedance on the grid side and the device side according to any one of claims 1 to 5 is implemented.

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