A method and system for testing the impedance of a flexible DC transmission line with adaptive adjustment of the harmonic frequency

Abstract

The application discloses a method and system for testing impedance of flexible direct current (DC) by self-adapting harmonic frequency, and belongs to the technical field of impedance testing. The method comprises the following steps: collecting three-phase voltage and three-phase current of the port; performing operation on the three-phase voltage and three-phase current based on a preset algorithm to obtain impedance amplitude and phase at a frequency point of a harmonic injected by a target flexible DC power transmission system this time; determining an average change rate of the impedance amplitude according to impedance amplitude and phase characteristics, taking the average change rate of the impedance amplitude as a discrimination object to determine a change step of a harmonic frequency injected by the target flexible DC power transmission system in a next calculation period, and self-adapting the harmonic injected into the flexible DC power transmission system according to the change step. The application adjusts the harmonic frequency injected into the flexible DC power transmission system according to the change step, and can improve the scanning efficiency of wideband impedance of the flexible DC power transmission system.

Description

Technical Field

[0001] This invention relates to the field of impedance testing technology, and more specifically, to a flexible DC impedance testing method and system that adaptively adjusts harmonic frequencies. Background Technology

[0002] Flexible DC transmission technology is a new generation of power transmission technology. Compared with traditional grid-based phase-commutation converter-based power transmission technology, it has advantages such as flexibility, high reliability, and island power supply. It is suitable for the efficient consumption of large-scale renewable energy, the construction of regional power transmission networks and efficient power distribution networks in large cities and islands.

[0003] In recent years, the system oscillation problem caused by flexible DC transmission has become increasingly prominent. The oscillation stability problems that have occurred in many flexible DC transmission projects at home and abroad have complex mechanisms and have brought huge risks to the safe operation of the power grid. Therefore, it is urgent and necessary to study the oscillation characteristics of flexible DC transmission systems.

[0004] Impedance analysis has become an important tool for studying the stability of interactive coupling systems between flexible DC transmission lines, power grids, and renewable energy power plants. In industry, impedance scanning is primarily used to obtain the impedance characteristics of different target systems, and the Nyquist criterion is employed to analyze the impedance relationships between these systems, studying system oscillation characteristics and oscillation suppression measures. To obtain accurate impedance characteristics, the frequency step size injected into the target system needs to be minimized; a commonly used step size is 1 Hz. Oscillations in flexible DC transmission projects exhibit broadband characteristics, and the impedance scanning frequency typically ranges from 1 Hz to 2400 Hz. According to Shannon's sampling theorem, using a 1 Hz frequency step size, the injection time for harmonic frequencies requires at least 2 seconds. In actual impedance scanning, the injection time for harmonics at each frequency point is typically 3 seconds. Therefore, current methods for scanning the broadband characteristics of flexible DC transmission systems suffer from low efficiency. Summary of the Invention

[0005] To address the above problems, this invention proposes a flexible DC impedance testing method that adaptively adjusts harmonic frequencies, characterized in that the method includes: Under the condition that the target flexible DC transmission system is in steady-state operation, after injecting harmonic current into the test port of the target flexible DC transmission system, the three-phase voltage and three-phase current of the port are collected. Based on a preset algorithm, the three-phase voltage and three-phase current are calculated to obtain the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of injected harmonics. Based on the impedance amplitude and phase characteristics, the average rate of change of the impedance amplitude is determined. The average rate of change of the impedance amplitude is used as the discrimination object to determine the step size of the harmonic frequency injected into the target flexible DC transmission system in the next calculation cycle. The harmonics injected into the flexible DC transmission system are adaptively adjusted according to the step size to test the impedance of the flexible DC transmission system.

[0006] Optionally, the method also includes adjusting key parameters related to a preset algorithm before injecting harmonic current.

[0007] Optional key parameters include: calculation period, minimum frequency of injected harmonic frequency, initial frequency, upper limit threshold of harmonic frequency and initial frequency change step size, injection time, amplitude, frequency change step size coefficient of different taps and limit of impedance amplitude change rate of different taps for each frequency point of the target flexible DC transmission system. The frequency change step size coefficients for different gears include: the frequency change step size coefficient for the first gear, the frequency change step size coefficient for the second gear, the frequency change step size coefficient for the third gear, the frequency change step size coefficient for the fourth gear, the frequency change step size coefficient for the fifth gear, and the frequency change step size coefficient for the sixth gear. The limits for the impedance amplitude change rate at different levels include: the impedance amplitude change rate at the first level, the impedance amplitude change rate at the second level, the impedance amplitude change rate at the third level, the impedance amplitude change rate at the fourth level, and the impedance amplitude change rate at the fifth level.

[0008] Optionally, the injected harmonic current is the nth harmonic current with a preset injection duration, frequency, and amplitude, where n is greater than 0.

[0009] Optionally, the calculations for the three-phase voltages and three-phase currents include: Using the Fourier transform formula, the amplitude and phase of the voltage and the amplitude and phase of the current are calculated based on the three-phase voltage and the three-phase current. Based on the amplitude and phase of the voltage and the amplitude and phase of the current, the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of the injected harmonics are calculated.

[0010] Optionally, determining the step size of the harmonic frequency variation injected in the next calculation cycle of the target flexible DC transmission system includes: If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the first range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the second range and less than the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the second range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the third position and less than the rate of change of impedance amplitude in the second position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the third position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fourth position and less than the rate of change of impedance amplitude in the third position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fourth position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fifth position and less than the rate of change of impedance amplitude in the fourth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fifth position. If the average rate of change of impedance amplitude is less than the rate of change of impedance amplitude in the fifth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the sixth position.

[0011] This invention also proposes a flexible DC impedance testing system that adaptively adjusts harmonic frequencies, comprising: The acquisition unit, under the condition that the target flexible DC transmission system is in steady-state operation, injects harmonic current into the measured port of the target flexible DC transmission system and then acquires the three-phase voltage and three-phase current of the port. The calculation unit, based on a preset algorithm, performs calculations on the three-phase voltage and three-phase current to obtain the impedance amplitude and phase at the frequency point of the injected harmonics in the target flexible DC transmission system. The adjustment unit determines the average rate of change of the impedance amplitude based on the impedance amplitude and phase characteristics. It uses the average rate of change of the impedance amplitude as a discrimination object to determine the step size of the harmonic frequency injected into the target flexible DC transmission system in the next calculation cycle. Based on the step size, it adaptively adjusts the harmonics injected into the flexible DC transmission system to test the impedance of the flexible DC transmission system.

[0012] Optionally, the system also includes a parameter adjustment unit for adjusting key parameters related to the preset algorithm before injecting harmonic current.

[0013] Optional key parameters include: calculation period, minimum frequency of injected harmonic frequency, initial frequency, upper limit threshold of harmonic frequency and initial frequency change step size, injection time, amplitude, frequency change step size coefficient of different taps and limit of impedance amplitude change rate of different taps for each frequency point of the target flexible DC transmission system. The frequency change step size coefficients for different gears include: the frequency change step size coefficient for the first gear, the frequency change step size coefficient for the second gear, the frequency change step size coefficient for the third gear, the frequency change step size coefficient for the fourth gear, the frequency change step size coefficient for the fifth gear, and the frequency change step size coefficient for the sixth gear. The limits for the impedance amplitude change rate at different levels include: the impedance amplitude change rate at the first level, the impedance amplitude change rate at the second level, the impedance amplitude change rate at the third level, the impedance amplitude change rate at the fourth level, and the impedance amplitude change rate at the fifth level.

[0014] Optionally, the injected harmonic current is the nth harmonic current with a preset injection duration, frequency, and amplitude, where n is greater than 0.

[0015] Optionally, the calculations for the three-phase voltages and three-phase currents include: Using the Fourier transform formula, the amplitude and phase of the voltage and the amplitude and phase of the current are calculated based on the three-phase voltage and the three-phase current. Based on the amplitude and phase of the voltage and the amplitude and phase of the current, the impedance amplitude and phase of the target flexible DC transmission system at any frequency point are calculated.

[0016] Optionally, determining the step size of the harmonic frequency variation injected in the next calculation cycle of the target flexible DC transmission system includes: If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the first range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the second range and less than the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the second range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the third position and less than the rate of change of impedance amplitude in the second position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the third position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fourth position and less than the rate of change of impedance amplitude in the third position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fourth position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fifth position and less than the rate of change of impedance amplitude in the fourth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fifth position. If the average rate of change of impedance amplitude is less than the rate of change of impedance amplitude in the fifth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the sixth position.

[0017] In another aspect, the present invention also provides a computing device, comprising: one or more processors; A processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, the method described above is implemented.

[0018] In another aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements the method described above.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides an impedance testing method for adaptively adjusting the harmonic frequency injected into a flexible DC transmission system. The method includes: injecting harmonic current into the test port of the target flexible DC transmission system under steady-state operation, and then collecting the three-phase voltage and three-phase current at the port; calculating the three-phase voltage and current based on a preset algorithm to obtain the impedance amplitude and phase at the frequency point of the injected harmonics; determining the average rate of change of the impedance amplitude based on the impedance amplitude and phase characteristics, using the average rate of change of the impedance amplitude as a criterion to determine the step size of the harmonic frequency injection in the next calculation cycle of the target flexible DC transmission system, and adaptively adjusting the harmonics injected into the flexible DC transmission system according to the step size. This invention, by adjusting the harmonics injected into the flexible DC transmission system based on the step size, can improve the scanning efficiency of the broadband impedance of the flexible DC transmission system. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the flexible DC impedance testing system used in an embodiment of the present invention; Figure 3 This is a flowchart of an embodiment of the present invention; Figure 4 This is a waveform diagram of the average rate of change of the amplitude of the flexible DC impedance according to an embodiment of the present invention; Figure 5 This is a waveform diagram showing the harmonic frequency variation step size according to an embodiment of the present invention; Figure 6 This is a waveform diagram of the harmonic frequency in an embodiment of the present invention; Figure 7 This is a comparison chart of impedance scanning results from an embodiment of the present invention; Figure 8 This is a structural diagram of the system of the present invention. Detailed Implementation

[0021] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0022] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0023] Example 1: This invention proposes an adaptive method for testing flexible DC impedance by adjusting harmonic frequencies, such as... Figure 1 As shown, it includes: Step 1: Under the condition that the target flexible DC transmission system is in steady-state operation, inject harmonic current into the test port of the target flexible DC transmission system, and then collect the three-phase voltage and three-phase current of the port. Step 2: Based on a preset algorithm, calculate the three-phase voltage and three-phase current to obtain the impedance amplitude and phase at the frequency point of the injected harmonics in the target flexible DC transmission system. Step 3: Based on the impedance amplitude and phase characteristics, determine the average rate of change of the impedance amplitude. Use the average rate of change of the impedance amplitude as the discrimination object to determine the step size of the harmonic frequency injected into the target flexible DC transmission system in the next calculation cycle. Adaptively adjust the harmonics injected into the flexible DC transmission system according to the step size to test the impedance of the flexible DC transmission system.

[0024] Optionally, the method also includes adjusting key parameters related to a preset algorithm before injecting harmonic current.

[0025] Optional key parameters include: calculation period, minimum frequency of injected harmonic frequency, initial frequency, upper limit threshold of harmonic frequency and initial frequency change step size, injection time, amplitude, frequency change step size coefficient of different taps and limit of impedance amplitude change rate of different taps for each frequency point of the target flexible DC transmission system. The frequency change step size coefficients for different gears include: the frequency change step size coefficient for the first gear, the frequency change step size coefficient for the second gear, the frequency change step size coefficient for the third gear, the frequency change step size coefficient for the fourth gear, the frequency change step size coefficient for the fifth gear, and the frequency change step size coefficient for the sixth gear. The limits for the impedance amplitude change rate at different levels include: the impedance amplitude change rate at the first level, the impedance amplitude change rate at the second level, the impedance amplitude change rate at the third level, the impedance amplitude change rate at the fourth level, and the impedance amplitude change rate at the fifth level.

[0026] Optionally, the injected harmonic current is the nth harmonic current with a preset injection duration, frequency, and amplitude, where n is greater than 0.

[0027] Optionally, the calculations for the three-phase voltages and three-phase currents include: Using the Fourier transform formula, the amplitude and phase of the voltage and the amplitude and phase of the current are calculated based on the three-phase voltage and the three-phase current. Based on the amplitude and phase of the voltage and the amplitude and phase of the current, the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of the injected harmonics are calculated.

[0028] Optionally, determining the step size of the harmonic frequency variation injected into the target flexible DC transmission system in the next calculation cycle includes: If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the first range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the second range and less than the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the second range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the third position and less than the rate of change of impedance amplitude in the second position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the third position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fourth position and less than the rate of change of impedance amplitude in the third position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fourth position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fifth position and less than the rate of change of impedance amplitude in the fourth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fifth position. If the average rate of change of impedance amplitude is less than the rate of change of impedance amplitude in the fifth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the sixth position.

[0029] The following description, in conjunction with specific applications of the present invention, provides further details: The implementation steps include: 1) A flexible DC impedance testing method with adaptive tuning frequency and key system parameters The key parameters in the proposed algorithm mainly include: computation cycle. T c minimum frequency f 0, initial frequency f init upper limit threshold of harmonic frequency f upth Initial frequency change step size D f 0, injection time per frequency point t inject The amplitude of the injected harmonic current I m Frequency variation step size coefficient for different gear levels K 0、 K 1. K 2. K 3. K 4 and K 5. Limits on the rate of change of impedance amplitude for different ranges. th1 l th2 l th3 l th4 and l th5 .

[0030] 2) Calculate the impedance amplitude and phase characteristics of the flexible DC at a specific frequency. Under the condition that the system under test is already in steady-state operation, for the k-th frequency point, the duration of the port injection is... t inject The frequency is f n_k The amplitude is I n_k The nth harmonic current is obtained, and the three-phase voltage and three-phase current at the port of the system under test are collected; the amplitude of the voltage is calculated using the Fourier transform formula (1). M n_vol_k and phase f n_vol_k and the amplitude of the current M n_cur_k and phase f n_cur_k The frequency is calculated using formula (2). f n_k Impedance amplitude of flexible DC transmission systemM n_Z_k and phase f n_Z_k .

[0031] in, f ( t () represents the voltage or current signal at the port of the system under test. w 0=2p f 0, T 0 = 1 / f 0, n This represents the harmonic order.

[0032] (1) (2) 3) Based on the average rate of change of impedance amplitude l ave Calculate the frequency change step size D f Calculate the (k+1)th frequency point, at the injection frequency of f m_k+1 Impedance amplitude of flexible DC transmission system under m-th harmonic current M m_Z_k+1 and phase f m_Z_k+1 The formula for calculating the rate of change of impedance amplitude l1 is: l1 = |( M m_Z_k+1 - M n_Z_k ) / (mn)|。 Calculate the (k+2)th frequency point, at the injection frequency of f p_k+2 Impedance amplitude of flexible DC transmission system under p-th harmonic current M p_Z_k+2 and phase f p_Z_k+2 The formula for calculating the rate of change of impedance amplitude l2 is: l2 = |( M p_Z_k+2 - M m_Z_k+1 ) / (pm)|。 Average rate of change of impedance amplitude l ave = (l1+l2) / 2.

[0033] Frequency variation step size D f Specific calculation method: When l ave ≥l th1 When, then D f=K 0D f 0; When l th2 ≤l ave <l th1 Then D f=K 1D f 0; When l th3 ≤l ave <l th2 Then D f=K 2D f 0; When l th4 ≤l ave <l th3 Then D f=K 3D f 0; When l th5 ≤l ave <l th4 Then D f=K 4D f 0; When l ave <l th5 Then D f=K 5D f 0.

[0034] 4) Calculate the frequency of the injected harmonic current, generate three-phase harmonic current signals, and inject them into the system under test using a controlled current source. The harmonic current frequency at the k-th frequency point f current_k From the initial frequency f init The harmonic current frequency at the (k-1)th frequency point f current_old_k-1 and the step size D of the change at the k-th frequency point f k According to formula (3), the result is as follows: (3) Based on the amplitude of harmonic current I m This allows us to obtain three-phase positive-sequence or negative-sequence currents.

[0035] This invention has been applied to the simulation study of the Zhangbei Flexible DC Power Grid Project. Based on the typical primary circuit and control parameters of the Zhangbei Flexible DC Power Grid Project, a simulation model was built. Figure 2 The simulation model shown employs an islanded voltage-frequency (VF) control strategy at the sending end and a constant DC voltage control strategy at the receiving end. The impedance characteristics of the flexible DC transmission system are obtained by injecting harmonic current into the islanded station and collecting PCC bus voltage and current scans.

[0036] The flowchart of the method for improving the broadband impedance scanning efficiency of flexible DC transmission systems based on adaptive adjustment of the frequency variation step size of injected harmonics described in this invention is as follows: Figure 3 As shown, the specific steps are as follows: 1) A flexible DC impedance testing method with adaptive tuning frequency and key system parameters Based on the above simulation prerequisites, the tuning values ​​for the key parameters are: calculation period. T c =3s, fundamental frequency f 0 = 1Hz, initial frequency f init =1Hz, initial frequency change step size D f 0 = 1Hz, injection time at each frequency point t inject =3Hz, amplitude of injected harmonic current I m =30A, frequency variation step size coefficient for different gears K 0=1 K 1=2、 K 2=5、 K 3=10、 K 4=20 and K 5=50, the limit of the rate of change of impedance amplitude for different ranges. th1 =0.5、l th2 =0.2、l th3 =0.05、l th4 =0.03 and l th5 =0.01.

[0037] 2) Calculate the impedance amplitude and phase characteristics of the flexible DC at a specific frequency. Taking 55Hz as an example, under the condition that the system under test is already in steady-state operation, the duration of the injection at its port is... t inject =3s, frequency is f 55_k =55Hz, amplitude is I 55_k =30A 55th harmonic current, and collect the three-phase voltage and three-phase current at the port of the system under test; calculate the amplitude and phase of the voltage and the amplitude and phase of the current using Fourier transform formula (1), and calculate the frequency using formula (2). f 55_k Impedance amplitude of flexible DC transmission system at 55Hz M 55_Z_k =35.3dB and phase f 55_Z_k =0.55°.

[0038] 3) Based on the average rate of change of impedance amplitude l ave Calculate the frequency change step size D f calculate f 55_kThe previous frequency point of 55Hz is f 53_k-1 =53Hz, corresponding to the impedance amplitude of the flexible DC transmission system M 53_Z_k-1 =35.74dB and phase f m_Z_k-1 =1.02°. The formula for calculating the impedance amplitude change rate l1 is: l1=|(35.3-35.74) / (55-53)|=0.22. Similarly, calculate the (k-2)th frequency point. f 52_k-2 =52Hz flexible DC transmission system impedance amplitude M 52_Z_k-2 and phase f 52_Z_k-2 The formula for calculating the rate of change of impedance amplitude, l2, is: l2 = |(35.74-36.11) / (53-52)| = 0.37. The average rate of change of impedance amplitude, l... ave = (l1+l2) / 2 = 0.295.

[0039] Based on the frequency change step size D f Specific calculation method: When l ave ≥l th1 When, then D f=K 0D f 0; When l th2 ≤l ave <l th1 Then D f=K 1D f 0; When l th3 ≤l ave <l th2 Then D f=K 2D f 0; When l th4 ≤l ave <l th3 Then D f=K 3D f 0; When l th5 ≤l ave <l th4 Then D f=K 4D f 0; When l ave <l th5 Then D f=K 5D f 0.

[0040] It can be seen that the frequency change step size D f=2Hz, 4) Calculate the frequency of the injected harmonic current, generate three-phase harmonic current signals, and inject them into the system under test using a controlled current source. The harmonic current frequency at the (k+1)th frequency point f current_k+1 From the initial frequency f init =1Hz, the harmonic current frequency at the k-th frequency point f current_old_k =55Hz and the step size D of the kth frequency point f k =2Hz is obtained according to formula (3) f current_k+1 =57Hz. Based on the harmonic current amplitude. I m =30A, which can obtain three-phase positive sequence or negative sequence current signals.

[0041] Through such Figure 6 The harmonic current source of the flexible DC impedance test system shown is injected into the flexible DC system, thereby cyclically calculating the impedance of the flexible DC system in the range of 1Hz to 2400Hz. This invention can significantly improve the broadband impedance scanning efficiency of flexible DC transmission systems by using a frequency adaptive adjustment method based on the impedance amplitude change rate in a 1Hz to 2400Hz wideband impedance characteristic scanning process, while ensuring the accuracy of the scanning results.

[0042] The effects of this invention are as follows: Figure 4 -Appendix Figure 7 As shown, the broadband impedance characteristics of a flexible DC transmission system from 1Hz to 2400Hz can be obtained by collecting data for 300 seconds. Compared with the traditional scanning method with a fixed frequency variation step of 1Hz, the data acquisition time is shortened by 6900 seconds, approximately 95.8%. Figure 7 It can be seen that the impedance scanning results of the method proposed in this invention are highly consistent with the traditional scanning method with a fixed 1Hz frequency variation step size, thus verifying the effectiveness of this invention.

[0043] Example 2: The present invention also provides a flexible DC impedance testing system 200 that adaptively adjusts harmonic frequencies, such as... Figure 8 As shown, it includes: The acquisition unit 201, under the condition that the target flexible DC transmission system is in steady-state operation, injects harmonic current into the measured port of the target flexible DC transmission system and then acquires the three-phase voltage and three-phase current of the port. The calculation unit 202 calculates the three-phase voltage and three-phase current based on a preset algorithm to obtain the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of injected harmonics. The adjustment unit 203 determines the average rate of change of the impedance amplitude based on the impedance amplitude and phase characteristics, uses the average rate of change of the impedance amplitude as a discrimination object to determine the step size of the harmonic frequency injected into the target flexible DC transmission system in the next calculation cycle, and adaptively adjusts the harmonics injected into the flexible DC transmission system according to the step size to test the impedance of the flexible DC transmission system.

[0044] The parameter adjustment unit 204 is used to adjust key parameters related to the preset algorithm before injecting harmonic current.

[0045] Key parameters include: calculation period, minimum frequency of injected harmonic frequency, initial frequency, upper limit threshold of harmonic frequency and initial frequency change step size, injection time and amplitude of injected harmonic current at each frequency point of the target flexible DC transmission system, frequency change step size coefficient of different levels and limit of impedance amplitude change rate of different levels. The frequency change step size coefficients for different gears include: the frequency change step size coefficient for the first gear, the frequency change step size coefficient for the second gear, the frequency change step size coefficient for the third gear, the frequency change step size coefficient for the fourth gear, the frequency change step size coefficient for the fifth gear, and the frequency change step size coefficient for the sixth gear. The limits for the impedance amplitude change rate at different levels include: the impedance amplitude change rate at the first level, the impedance amplitude change rate at the second level, the impedance amplitude change rate at the third level, the impedance amplitude change rate at the fourth level, and the impedance amplitude change rate at the fifth level.

[0046] The injected harmonic current is the nth harmonic current with a preset injection duration, frequency, and amplitude, where n is greater than 0.

[0047] The calculation of the three-phase voltage and three-phase current includes: Using the Fourier transform formula, the amplitude and phase of the voltage and the amplitude and phase of the current are calculated based on the three-phase voltage and the three-phase current. Based on the amplitude and phase of the voltage and the amplitude and phase of the current, the impedance amplitude and phase at the frequency point where the target flexible DC transmission system is injected with harmonics are calculated.

[0048] The step size for determining the variation of the harmonic frequency injected at any frequency point of the target flexible DC transmission system includes: If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the first range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the second range and less than the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the second range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the third position and less than the rate of change of impedance amplitude in the second position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the third position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fourth position and less than the rate of change of impedance amplitude in the third position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fourth position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fifth position and less than the rate of change of impedance amplitude in the fourth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fifth position. If the average rate of change of impedance amplitude is less than the rate of change of impedance amplitude in the fifth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the sixth position.

[0049] Example 3: Based on the same inventive concept, this invention also provides a computer device, which includes a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement corresponding method flows or corresponding functions, thereby implementing the steps of the methods in the above embodiments.

[0050] Example 4: Based on the same inventive concept, this invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device used to store programs and data. It is understood that the computer-readable storage medium here can include both the built-in storage medium in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, this storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions can be one or more computer programs (including program code). It should be noted that the computer-readable storage medium here can be high-speed RAM or non-volatile memory, such as at least one disk storage device. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the method in the above embodiments.

[0051] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0052] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0053] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0054] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0055] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0056] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for adaptively adjusting harmonic frequencies in testing flexible DC impedance, characterized in that, The method includes: Under the condition that the target flexible DC transmission system is in steady-state operation, after injecting harmonic current into the test port of the target flexible DC transmission system, the three-phase voltage and three-phase current of the port are collected. Based on a preset algorithm, the three-phase voltage and three-phase current are calculated to obtain the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of this injected harmonic. Based on the impedance amplitude and phase, the average rate of change of the impedance amplitude is determined. The average rate of change of the impedance amplitude is used as the discrimination object to determine the step size of the harmonic frequency injected into the target flexible DC transmission system in the next calculation cycle. The harmonics injected into the flexible DC transmission system are adaptively adjusted according to the step size to test the impedance of the flexible DC transmission system. The step size for determining the change in harmonic frequency injected in the next calculation cycle of the target flexible DC transmission system includes: If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the first range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the second range and less than the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the second range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the third position and less than the rate of change of impedance amplitude in the second position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the third position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fourth position and less than the rate of change of impedance amplitude in the third position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fourth position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fifth position and less than the rate of change of impedance amplitude in the fourth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fifth position. If the average rate of change of impedance amplitude is less than the rate of change of impedance amplitude in the fifth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the sixth position.

2. The method according to claim 1, characterized in that, The method further includes adjusting key parameters related to a preset algorithm before injecting harmonic current.

3. The method according to claim 2, characterized in that, The key parameters include: calculation period, minimum frequency of injected harmonic frequency, initial frequency, upper limit threshold of harmonic frequency and initial frequency change step size, injection time, amplitude, frequency change step size coefficient of different levels and limit of impedance amplitude change rate of different levels of the injected harmonic current at each frequency point of the target flexible DC transmission system. The frequency change step size coefficients for different gears include: the frequency change step size coefficient for the first gear, the frequency change step size coefficient for the second gear, the frequency change step size coefficient for the third gear, the frequency change step size coefficient for the fourth gear, the frequency change step size coefficient for the fifth gear, and the frequency change step size coefficient for the sixth gear. The limits for the impedance amplitude change rate at different levels include: the impedance amplitude change rate at the first level, the impedance amplitude change rate at the second level, the impedance amplitude change rate at the third level, the impedance amplitude change rate at the fourth level, and the impedance amplitude change rate at the fifth level.

4. The method according to claim 1, characterized in that, The injected harmonic current is the nth harmonic current with a preset injection duration, frequency, and amplitude, where n is greater than 0.

5. The method according to claim 1, characterized in that, The calculation of the three-phase voltage and three-phase current includes: Using the Fourier transform formula, the amplitude and phase of the voltage and the amplitude and phase of the current are calculated based on the three-phase voltage and the three-phase current. Based on the amplitude and phase of the voltage and the amplitude and phase of the current, the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of the injected harmonics are calculated.

6. A flexible DC impedance testing system with adaptive harmonic frequency adjustment, characterized in that, The system includes: The acquisition unit, under the condition that the target flexible DC transmission system is in steady-state operation, injects harmonic current into the measured port of the target flexible DC transmission system and then acquires the three-phase voltage and three-phase current of the port. The calculation unit, based on a preset algorithm, performs calculations on the three-phase voltage and three-phase current to obtain the impedance amplitude and phase at the frequency point of the injected harmonics in the target flexible DC transmission system. The adjustment unit determines the average rate of change of the impedance amplitude based on the impedance amplitude and phase, uses the average rate of change of the impedance amplitude as a discrimination object to determine the step size of the harmonic frequency injected into the target flexible DC transmission system in the next calculation cycle, and adaptively adjusts the harmonics injected into the flexible DC transmission system according to the step size to test the impedance of the flexible DC transmission system. The step size for determining the change in harmonic frequency injected in the next calculation cycle of the target flexible DC transmission system includes: If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the first range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the second range and less than the rate of change of impedance amplitude in the first range, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the second range. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the third position and less than the rate of change of impedance amplitude in the second position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the third position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fourth position and less than the rate of change of impedance amplitude in the third position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fourth position. If the average rate of change of impedance amplitude is greater than or equal to the rate of change of impedance amplitude in the fifth position and less than the rate of change of impedance amplitude in the fourth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the fifth position. If the average rate of change of impedance amplitude is less than the rate of change of impedance amplitude in the fifth position, then the change step size is the product of the initial frequency change step size and the frequency change step size coefficient of the sixth position.

7. The system according to claim 6, characterized in that, The system also includes a parameter adjustment unit, used to adjust key parameters related to a preset algorithm before injecting harmonic current.

8. The system according to claim 7, characterized in that, The key parameters include: calculation period, minimum frequency of injected harmonic frequency, initial frequency, upper limit threshold of harmonic frequency and initial frequency change step size, injection time, amplitude, frequency change step size coefficient of different levels and limit of impedance amplitude change rate of different levels of the injected harmonic current at each frequency point of the target flexible DC transmission system. The frequency change step size coefficients for different gears include: the frequency change step size coefficient for the first gear, the frequency change step size coefficient for the second gear, the frequency change step size coefficient for the third gear, the frequency change step size coefficient for the fourth gear, the frequency change step size coefficient for the fifth gear, and the frequency change step size coefficient for the sixth gear. The limits for the impedance amplitude change rate at different levels include: the impedance amplitude change rate at the first level, the impedance amplitude change rate at the second level, the impedance amplitude change rate at the third level, the impedance amplitude change rate at the fourth level, and the impedance amplitude change rate at the fifth level.

9. The system according to claim 6, characterized in that, The injected harmonic current is the nth harmonic current with a preset injection duration, frequency, and amplitude, where n is greater than 0.

10. The system according to claim 6, characterized in that, The calculation of the three-phase voltage and three-phase current includes: Using the Fourier transform formula, the amplitude and phase of the voltage and the amplitude and phase of the current are calculated based on the three-phase voltage and the three-phase current. Based on the amplitude and phase of the voltage and the amplitude and phase of the current, the impedance amplitude and phase of the target flexible DC transmission system at the frequency point of the injected harmonics are calculated.

11. A computer device, characterized in that, include: One or more processors; A processor is used to execute one or more programs; When the one or more programs are executed by the one or more processors, the method described in any one of claims 1-5 is implemented.

12. A computer-readable storage medium, characterized in that, It contains a computer program, which, when executed, implements the method as described in any one of claims 1-5.

Images